Welding method using special torch

Abstract

Provided is a welding method using a special torch and a flux cored wire, in which the special torch has a suction nozzle between the contact tip and the shield nozzle, and the flux cored wire has a flux filled inside the steel outer casing, and a seam portion where both ends of a metal in a width direction of the steel outer casing are butted or overlapped in a longitudinal direction of the flux cored wire.

The invention claimed is: 
     
       1. A welding method, comprising:
 performing welding by feeding a flux cored wire to protrude from a contact tip and produce a protruded portion, while discharging an electric current through the protruded portion of the flux cored wire, to form an electric arc and melt the protruded portion of the flux cored wire; 
 supplying a shielding gas from a shielding gas nozzle, to provide a gas shield around the protruded portion of the flux cored wire; and 
 sucking the shielding gas during the welding step using a suction nozzle provided between the contact tip and the shielding gas nozzle, 
 wherein the flux cored wire comprises:
 a steel outer casing, 
 a flux filled inside the steel outer casing, and 
 
 a seam portion of the steel outer casing where opposing ends of the steel outer casing in a width direction of the steel outer casing are butted or overlapped, the seam portion extending in a longitudinal direction of the flux cored wire, 
 wherein, in a cross section of the seam portion, when a length of a portion of a clearance between said ends of the steel outer casing where the size of the clearance is less than 20 μm is denoted by La, a length of a portion of said clearance where the size of the clearance is 20 μm or more and less than 40 μm is denoted by Lb, and a length of a portion of said clearance where the size of the clearance is 40 μm or more and less than 100 μm is denoted by Lc, a value represented by Lseam=2.0×La+1.5×Lb+Lc is 0.1 to 1.5 mm. 
 
     
     
       2. The welding method according to  claim 1 , wherein the flux cored wire has a wire diameter of 1.2 to 2.0 mm and a ratio of the flux to a total mass of the flux cored wire is 8 to 30 mass %. 
     
     
       3. The welding method according to  claim 1 , wherein the flux comprises a slag forming agent, the slag forming agent comprising at least one compound selected from the group consisting of a metal oxide, a metal fluoride and a metal carbonate and an impurity, and a ratio of the slag forming agent to the total mass of the flux cored wire is 3 to 21 mass %. 
     
     
       4. The welding method according to  claim 3 , wherein
 the slag forming agent comprises, in a ratio to the total mass of the flux cored wire: 
 3.5 to 20.5 mass % of the metal oxide; 
 0 to 0.5 mass % of the metal fluoride; and 
 0 to 0.5 mass % of the metal carbonate. 
 
     
     
       5. The welding method according to  claim 4 , wherein
 the metal oxide comprises, in a ratio to the total mass of the flux cored wire: 
 1.5 to 15.0 mass % of TiO 2 ; 
 0.15 to 4.0 mass % of SiO 2 ; 
 0 to 3.0 mass % of ZrO 2 ; 
 0 to 2.0 mass % of Al 2 O 3 ; and 
 0.01 to 0.8 mass % of (Na 2 O+K 2 O+Li 2 O). 
 
     
     
       6. The welding method according to  claim 3 , wherein
 the slag forming agent comprises, in a ratio to the total mass of the flux cored wire: 
 0 to 1.5 mass % of the metal oxide; 
 1.5 to 8.5 mass % of the metal fluoride; and 
 0 to 5.0 mass % of the metal carbonate. 
 
     
     
       7. The welding method according to  claim 6 , wherein
 the metal fluoride comprises, in a ratio to the total mass of the flux cored wire: 
 0 to 5.0 mass % of CaF 2 ; 
 0 to 5.0 mass % of BaF 2 ; 
 0 to 5.0 mass % of SrF 2 ; and 
 1.5 to 8.0 mass % of (CaF 2 +BaF 2 +SrF 2 ). 
 
     
     
       8. The welding method according to  claim 3 , wherein the metal carbonate comprises 0 to 5 mass % of (CaCO 3 +BaCO 3 ) in a ratio to the total mass of the flux cored wire. 
     
     
       9. The welding method according to  claim 1 , wherein
 a distance D t-b  along a longitudinal direction of the welding wire between a tip end of the contact tip and a base material in the special torch is 15 to 40 mm, and 
 a distance D t-k  along the longitudinal direction of the welding wire from the tip end of the contact tip to a tip end of the suction nozzle and the distance D t-b , satisfy relationships:
     D   t-k  (mm)≥0.3× D   t-b  (mm) and
 
     D   t-k  (mm)≤ D   t-b  (mm)−8.